1. Field of the Invention
The present invention relates to an ink composition for thermal transfer printing and a film for thermal printing such as an ink ribbon. More particularly, the present invention relates to improvement of a binder contained in an ink composition for thermal transfer printing.
2. Description of the Related Art
A film for thermal transfer printing is prepared by forming, on a substrate, a heat melting or softening ink layer which can be melt or softened by heat and transferred to other material (cf. Japanese Patent Kokai Publication No. 3919/1980). The ink layer can be heated with a thermal head or by Joule heat generated by applying an electric current through the substrate, and the substrate is so constructed as to be suitable for the heating manner.
However, heat transferred printing from the conventional films for thermal transfer printing have an insufficient durability of printing. For example, the printing is worn by mechanical friction, remelt or resoftened by frictional heat or increase of ambient temperature to lose their displaying function.